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// G4FSALDormandPrince745
//
// Class description:
//
// DormandPrince7 - 5(4) FSAL stepper

// Created: Somnath Banerjee, Google Summer of Code 2015, 25 May 2015
// Supervision: John Apostolakis, CERN
// --------------------------------------------------------------------
#ifndef G4FSALDORMANDPRINCE745_HH
#define G4FSALDORMANDPRINCE745_HH

#include "G4VFSALIntegrationStepper.hh"

class G4FSALDormandPrince745 : public G4VFSALIntegrationStepper
{
  public:

    G4FSALDormandPrince745(G4EquationOfMotion* EqRhs,
                           G4int numberOfVariables = 6,
                           G4bool primary = true);
   ~G4FSALDormandPrince745();

    G4FSALDormandPrince745(const G4FSALDormandPrince745&) = delete;
    G4FSALDormandPrince745& operator=(const G4FSALDormandPrince745&) = delete;

    void Stepper( const G4double y[],
                  const G4double dydx[],
                        G4double h,
                        G4double yout[],
                        G4double yerr[],
                        G4double nextDydx[]) ;
    void interpolate( const G4double yInput[],
                      const G4double dydx[],
                            G4double yOut[],
                            G4double Step,
                            G4double tau ) ;

    void SetupInterpolate( const G4double yInput[],
                           const G4double dydx[],
                           const G4double Step );
      // For higher order Interpolant
    
    void Interpolate( const G4double yInput[],
                      const G4double dydx[],
                      const G4double Step,
                            G4double yOut[],
                            G4double tau );
      // For calculating the output at the tau fraction of Step
    

    G4double  DistChord()   const;
    inline G4int IntegratorOrder() const {return 4; }
    inline G4bool isFSAL() const { return true; }
    
  private:
    
    G4double *ak2, *ak3, *ak4, *ak5, *ak6, *ak7,
             *ak8, *ak9,         // For additional stages in the interpolant
             *yTemp, *yIn;
    
    G4double* pseudoDydx_for_DistChord;
      // Only for use with DistChord()
    
    G4double fLastStepLength = -1.0;
    G4double *fLastInitialVector, *fLastFinalVector,
             *fInitialDyDx, *fLastDyDx, *fMidVector, *fMidError;
      // For DistChord() calculations
    
    G4FSALDormandPrince745* fAuxStepper = nullptr;
};

#endif